The present invention relates to a hot melt composition excellent in moistureproof properties, and recyclable moistureproof (laminated) paper using the same, which is excellent in disintegrating properties and moistureproof properties.
As moistureproof paper used as packaging paper for newsprint base paper and copying paper, paper coated with polyolefin polymers such as polyethylene and polypropylene have been widely used. The moistureproof paper coated with the polyolefin polymers have the advantages of excellent workability and moistureproof properties and low cost. However, when it is tried to recycle these paper to reuse them, the coating strength of moistureproof layers is too strong to sufficiently disintegrate the paper with a disintegrator in a pulping process. As a result, the olefinic resin layers separated from the paper remain in the pulp as films, which make it impossible to recycle used paper.
In recent years, as recyclable moistureproof paper, moistureproof paper have been proposed which are coated with emulsions comprising synthetic rubber latexes and wax emulsions, or synthetic rubber latexes, wax emulsions and resin emulsions. These moistureproof paper have good moistureproof properties, and also have recyclability. However, they have the disadvantage that a long and large drying apparatus is required and it causes poor productivity, because coating solutions are emulsions.
Further, recently, moistureproof paper coated with a moistureproof hot melt composition mainly composed of an amorphous poly-xcex1-olefin (hereinafter abbreviated as APAO), a tackifier resin and wax has been proposed (Japanese Patent Laid-open Publication (Hei) 09-316252 and Japanese Patent Laid-open Publication (Hei) 11-158330). This moistureproof paper is excellent in moistureproof properties and disintegrating properties, and moreover has the advantage that it can be produced at low cost, because inexpensive APAO is used as a main component. However, the APAO used as a main component is amorphous and soft, so that the coated moistureproof paper is liable to show tackiness. Inhibition of the tackiness tends to bring cracks on a moistureproof layer when the paper is folded. It is therefore difficult to balance various properties. Further, the melt viscosity of the moistureproof hot melt composition is low, so that application thereof to T-die extrusion coating is difficult. Thus, there is a limitation on a coating method of the composition.
It is therefore an object of the present invention to provide a hot melt composition excellent in moistureproof properties.
Another object of the present invention is to provide moistureproof paper using the same, which is excellent in moistureproof properties and recyclability, low in cost and excellent in productivity.
According to the present invention, there is provided
(1) a composition comprising 20% to 90% by weight of polyethylene and/or polypropylene (A) and 10% to 80% by weight of a tackifier resin (B), with the proviso that (A)+(B)=100% by weight (hereinafter also referred as to xe2x80x9ccomposition (1)xe2x80x9d);
(2) a composition comprising 20% to 90% by weight of the above-mentioned component (A), 5% to 80% by weight of the above-mentioned component (B) and 0.1% to 50% by weight of wax (C), with the proviso that (A)+(B)+(C)=100% by weight (hereinafter also referred as to xe2x80x9ccomposition (2)xe2x80x9d);
(3) a composition comprising 10% to 90% by weight of an ethylene-vinyl acetate copolymer (D) (hereinafter also referred to as xe2x80x9cEVAxe2x80x9d) and 10% to 90% of the above-mentioned component (B), with the proviso that (D)+(B)=100% by weight (hereinafter also referred as to xe2x80x9ccomposition (3)xe2x80x9d); or
(4) a composition comprising 10% to 90% by weight of the above-mentioned component (D), 5% to 90% by weight of the above-mentioned component (B) and 0.1% to 50% of the above-mentioned component (C), with the proviso that (D)+(B)+(C)=100% by weight (hereinafter also referred as to xe2x80x9ccomposition (4)xe2x80x9d).
In the moistureproof hot melt composition of the present invention, polyethylene and/or polypropylene (A) or the EVA (D) is used as a base polymer, with which the tackifier resin (B) and/or the wax (C) is further mixed. Accordingly, when the moistureproof hot melt composition is used, the film strength of a moistureproof layer can be kept lower than that of the conventional moistureproof paper with which olefinic polymers are used. It is also possible to achieve disintegration of used paper with a disintegrator in a pulping process on recycling. These polymers (A) or (D) have appropriate hardness and softness, so that various properties required for the moistureproof hot melt composition can be easily balanced, and the MFR (Melt Flow Rate) of the moistureproof hot melt composition can be freely adjusted. Accordingly, the moistureproof hot melt composition of the present invention is applicable to various coaters.
The MFR will be described in detail below.
The MFR is generally used for indicating the fluidity of a resin.
The MFR value is determined by the following method. As to polyethylene or EVA, a material is put in a cylinder having an orifice with a diameter of 2.1 mm and a length of 8 mm, and the material melted is extruded at 190xc2x0 C. (230xc2x0 C. for polypropylene) under a load of 2,160 g. The weight of the material extruded for 5 to 240 seconds is measured, and then, converted to gram per 10 minutes, thereby obtaining the MFR value. That is to say, the higher MFR value means the better fluidity (see JIS-K-7210).
The most preferable MFR value of polyethylene and polypropylene (A) used in the present invention varies depending on the coating method of the moistureproof hot melt composition. For example, in T-die extrusion coating, the MFR is preferably from 0.1 to 200 g/10 minutes, more preferably from 0.1 to 50 g/10 minutes, and particularly preferably from 0.1 to 30 g/10 minutes. On the other hand, in coating with a head coater or a roll coater, the MFR is preferably from 30 to 2,000 g/10 minutes, and more preferably from 50 to 2,000 g/10 minutes. It is difficult to obtain polyethylene and polypropylene having an MFR exceeding 2,000 g/10 minutes or less than 0.1 g/10 minutes from the market.
It is preferred that polyethylene constituting component (A) has a tensile breaking strength (in accordance with JIS K6760) of 9.8 to 1,960 N/cm2 (1 to 200 kgf/cm2). When polyethylene having a tensile breaking strength exceeding 1,960 N/cm2 is used, the film strength of the moistureproof hot melt composition of the present invention is increased, resulting in a tendency to poor disintegrating properties.
The compounding ratio of polyethylene and/or polypropylene (A) is from 20% to 90% by weight, preferably from 30% to 80% by weight, and more preferably from 40% to 80% by weight, for a two-component system (composition (1)). When the compounding ratio is less than 20% by weight, a moistureproof layer is liable to have a crack when folded. On the other hand, exceeding 90% by weight results in poor disintegrating properties.
For a three-component system (composition (2)), the compounding ratio thereof is from 20% to 90% by weight, preferably from 30% to 80% by weight, and more preferably from 40% to 70% by weight. When the compounding ratio is less than 20% by weight, a moistureproof layer is liable to have a crack when folded. On the other hand, exceeding 90% by weight results in poor disintegrating properties.
The most preferable MFR of the EVA (D) used in the present invention varies depending on the coating method of the moistureproof hot melt composition and the vinyl acetate content of the EVA (D) . For example, in T-die extrusion coating, the MFR is preferably from 0.1 to 200 g/10 minutes, more preferably from 0.1 to 50 g/10 minutes, and particularly preferably from 0.1 to 30 g/10 minutes. On the other hand, in coating with a head coater or a roll coater, the MFR is preferably from 0.1 to 2,000 g/10 minutes, more preferably from 1 to 100 g/10 minutes, and particularly preferably from 1 to 50 g/10 minutes. When the vinyl acetate content of the EVA (D) is from 1% to 15% by weight, an MFR of more than 2,000 g/10 minutes results in the liability of pitch to adhere to a dryer in a drying process of recycling. On the other hand, when the vinyl acetate content exceeds 15% by weight, the range of the MFR within which the above-mentioned problem does not arise is from 0.1 to 100 g/10 minutes. Further, it is difficult to obtain the EVA having an MFR of less than 0.1 g/10 minutes from the market. However, even when the EVA has an MFR higher than 100 g/10 minutes, recycling by mixing it with a large amount of paper or corrugated fiberboard allows the hot melt composition to be dispersed in a large amount of paper. Consequently, pitch becomes difficult to adhere to a dryer to make it possible to use such an EVA.
The compounding ratio of the EVA (D) is from 10% to 90% by weight, and preferably from 25% to 70% by weight, for a two-component system (composition (3)). When the compounding ratio is less than 10% by weight, a moistureproof layer is liable to have a crack when folded. On the other hand, exceeding 90% by weight results in poor disintegrating properties.
For a three-component system (composition (4)), the compounding ratio thereof is from 10% to 90% by weight, and preferably from 25% to 60% by weight. When the compounding ratio is less than 10% by weight, a moisture proof layer is liable to have a crack when folded. On the other hand, exceeding 90% by weight results in poor disintegrating properties.
The tackifier resins (B) used in the present invention include terpene resins, aliphatic resins, aromatic resins, alicyclic resins, coumarone-indene resins, rosin and rosin derivatives etc. The tackifier resins (B) have an effect of enhancing the disintegrating properties and moistureproof properties of the hot melt compositions.
Of these, the terpene resins are resins mainly containing xcex1-pinene, xcex2-pinene and dipentene obtained from pine essential oil. Specific examples of the terpene resins include terpene resins obtained by polymerization of terpene essential oil, terpene-phenol resins and modified aromatic terpene resins.
The aliphatic resins are resins obtained by polymerization of aliphatic monomers formed by thermal decomposition of petroleum naphtha, and monomer sources include the C5 fraction, pentanes, isoprene and 1,3-pentadiene.
The aromatic resins are resins obtained by polymerization of aromatic monomers formed by thermal decomposition of petroleum naphtha, and monomer sources include the C9 fraction and styrenic compounds.
The alicyclic (petroleum) resins are resins having a structure in which carbon atoms are cyclically combined and not belonging to aromatic resins. And the alicyclic resins are produced by using high-purity dicyclopentadiene as a main raw material, obtained by distillation after decomposition of naphtha cracking products. In addition, the C9 fraction, ester-containing monomers and hydroxyl group-containing monomers are sometimes used for modification.
The alicyclic petroleum resins are produced by thermal polymerization or cationic polymerization of dicyclopentadiene. They have formerly been obtained by cationic polymerization of relatively low-purity dicyclopentadiene in many cases. Recently, however, they have been produced by thermal polymerization of high-purity dicyclopentadiene in many cases.
The coumarone-indene resins are relatively low molecular weight resins mainly composed of polymerization products of coumarone and indene.
The rosin is pale yellow to brown, hard and brittle resins having a softening point of 70 to 85xc2x0 C., and includes three kinds of gum rosin obtained from pine oleoresin collected from living pine trees as a raw material, wood rosin obtained by extraction with a petroleum solvent from pine stumps and tall oil rosin obtained from waste liquid in producing kraft pulp.
The rosin derivatives include rosin modified by hydrogenation, disproportionation or dimerization, and rosin esterified with various alcohols such as methanol, glycols, glycerol and pentaerythritol.
Although any of the above tackifier resins (B) maybe used, the terpene resins and the alicyclic resins are preferred because of their excellent moistureproof properties.
The compounding amount of the tackifier resin (B) is from 10% to 80% by weight, and preferably from 20% to 60% by weight, for the two-component system (composition (1)). For the three-component system (composition (2)), the compounding ratio of the tackifier resin is from 5% to 80% by weight, preferably from 5% to 60% by weight, and more preferably from 5% to 40% by weight.
Further, for the two-component system (composition (3)), the compounding amount thereof is from 10% to 90% by weight, and preferably from 20% to 70% by weight. For the tree-component system (composition (4)), the compounding ratio thereof is from 5% to 90% by weight, preferably from 5% to 70% by weight, and more preferably from 20% to 50% by weight.
When the compounding ratio of the tackifier resin (B) is less than the above-mentioned value, disintegrating properties and moistureproof properties are deteriorated. On the other hand, when the compounding ratio thereof exceeds the above-mentioned value, a moistureproof layer is liable to have a crack when folded.
The softening point (in accordance with JIS K6714) of the tackifier resin (B) is preferably from 70 to 190xc2x0 C., and more preferably from 100 to 190xc2x0 C. When the softening point is less than 70xc2x0 C., the tackiness is liable to appear, which causes pitch to adhere to a dryer in a drying process when processed moistureproof paper is recycled. On the other hand, it is difficult to obtain the resins having a softening point of higher than 190xc2x0 C. from the market.
The wax (C) used in the present invention includes paraffin wax, microcrystalline wax, carnauba wax, Fischer-Tropsch wax, polyethylene wax, polypropylene wax etc.
Of these, the paraffin wax means a crystalline paraffin hydrocarbon mixture contained in petroleum. A main component thereof is generally a straight chain paraffin having about 18 to about 30 carbon atoms. It has a molecular weight of 300 to 500, and a melting point/softening point of about 45 to about 70xc2x0 C.
The microcrystalline wax is a hydrocarbon of 30 to 60 carbon atoms extracted from the heavy lubricating oil fraction of petroleum, rich in non-straight chain components. It shows yellow, and variously changes in hardness and viscosity. It has a molecular weight of 450 to 700, and a melting point/softening point of about 70 to about 90xc2x0 C.
The carnauba wax is obtained by collecting a resin allowed to ooze out of leaves and leaf buds of carnauba palm trees, putting the resin into boiling water, and collecting a melt floating on the surface. It has a melting point/softening point of about 80 to about 86xc2x0 C., and a main component thereof is a cerotic acid ester of myricyl alcohol.
The Fischer-Tropsch wax is wax formed as a by-product in producing synthetic petroleum from coal by the Fischer-Tropsch process. It has a molecular weight of 800 to 1,300, and a melting point/softening point of about 95 to about 115xc2x0 C.
The polyethylene wax is wax obtained by direct polymerization of ethylene, thermal decomposition of low-density polyethylene or purification of a by-product formed in the production process of high-density polyethylene. It has a molecular weight of 500 to 8,000, and a melting point/softening point of about 100 to about 140xc2x0 C.
The polypropylene wax is wax obtained by direct polymerization of propylene or thermal decomposition of polypropylene. It has a molecular weight of about 3,000 to about 50,000.
The wax (C) has the effects of decreasing the tackiness of the hot melt composition and enhancing moistureproof properties. As the wax (C), any wax may be used. However, wax having a melting point of 100 to 170xc2x0 C. is preferably used. The use of wax having a melting point of less than 100xc2x0 C. results in the liability of pitch to adhere to a dryer in recycling process. On the other hand, it is difficult to obtain wax having a melting point of higher than 170xc2x0 C. from the market.
The compounding amount of the wax (C) is from 0.1% to 50% by weight, preferably from 5% to 40% by weight, and more preferably from 10% to 35% by weight, for the three-component system (composition (2)). For the three-component system (composition (4)), the compounding ratio thereof is from 0.1% to 50% by weight, preferably from 5% to 50% by weight, and more preferably from 10% to 40% by weight.
When the compounding ratio of the wax (C) is less than the above-mentioned value, the effect of inhibiting the tackiness of a moistureproof layer is not sufficiently exhibited, resulting in a performance substantially similar to that of the two-component system. On the other hand, when the compounding ratio thereof exceeds the above-mentioned value, the moistureproof layer is liable to have a crack when folded.
The moistureproof hot melt composition of the present invention is obtained by mixing the above-mentioned components (A) and (B) (composition (1)), components (A) to (C) (composition (2)), components (D) and (B) (composition (3)) or components (D), (B) and (C) (composition (4)). However, the composition of the present invention can contain an additive such as a filler, for example, calcium carbonate, titanium oxide, barium sulfate, talc, clay or carbon black, a lubricant, an anti-fogging agent, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, a plasticizer or oil, as long as it dose not impair the effects of the present invention. There is no particular limitation on these additives, and additives which have been used in the hot melt compositions and have hitherto been known are used.
Coaters used for the moistureproof hot melt composition of the present invention are not limited. Examples of them include such as a T-die extrusion coater, a roll coater and a head coater in which the composition melted by heating is used. In particular, the T-die extrusion coater is preferred, because fine coating films having no pinhole can be obtained at high speed and the thickness of the coating films can be easily decreased. The moistureproof hot melt composition of the present invention having a low MFR can be easily processed with the conventional T-die extrusion coater to produce moistureproof paper at low cost. When processed with the T-die extrusion coater, the moistureproof hot melt composition having an MFR of 1 to 500 g/10 minutes is used. The MFR is preferably from 1 to 300 g/10 minutes, more preferably from 1 to 200 g/10 minutes, and particularly preferably from 1 to 100 g/10 minutes. Using the composition having an MFR exceeding 500 g/10 minutes, it becomes difficult to process with the T-die extrusion coater because of too low melt viscosity thereof. On the other hand, using the composition having an MFR of less than 1 g/10 minutes, it becomes difficult to process it with the T-die extrusion coater because of too high melt viscosity thereof.
The melting temperature of the moistureproof hot melt composition of the present invention in melt coating is usually from 150 to 250xc2x0 C., and preferably from 180 to 230xc2x0 C. Although the coating amount is not particularly limited, it is usually from 5 to 40 g/m2, and preferably from 10 to 25 g/m2.
The moistureproof hot melt composition of the present invention having a low MFR can be continuously produced with an extruder suitably. On the other hand, the composition having a high MFR can be suitably produced with a blender or a kneader equipped with an extruder. However, there is no particular limitation on the method for producing the hot melt composition.
Coating types of the hot melt composition of the present invention include, but are not limited to coating on one side of paper, coating on both sides of paper and sandwich coating between paper and paper. Any coating types may be used.
Paper to be coated with the moistureproof hot melt composition of the present invention are not limited, and any paper may be used. Examples of them include such as unbleached kraft paper, bleached kraft paper, paperboard and liner paper. Although there is no particular limitation on the basis weight of paper, it is preferably from 50 to 200 g/m2.
The moistureproof paper coated with the moistureproof hot melt composition of the present invention has more excellent moistureproof properties than moistureproof paper coated with a conventional olefin resin such as polyethylene or polypropylene, and also has excellent disintegrating properties. In the present invention, inexpensive polyethylene and/or polypropylene or the EVA is used as the base polymer, so that the raw material cost can be lowered. Further, the moistureproof hot melt composition of the present invention is excellent in processability, and thin coating films having no pinhole can be obtained with any coater. By use of the moistureproof hot melt composition of the present invention, the processing cost can be lowered, thus the recyclable moistureproof paper can be supplied at a low price.
The present invention will be illustrated with reference to production examples and examples in more detail below, but these examples are not intended to limit the scope of the invention. Parts and percentages hereinafter used are on a weight basis, unless otherwise specified.
Components (A) and (D) were prepared as follows:
(A-1): Low-density polyethylene, a trial product (MFR: 1,000 g/10 minutes, density: 0.92 to 0.93 g/cm3)
(D-1): EVA, a trial product (MFR: 200 g/10 minutes, vinyl acetate content: 10%)